Impairments - Impairment Expense Table (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Impaired Long Lived Assets Held and Used [Line Items]
Total impairment expense	$ 4	$ 183	$ 166	$ 287
Oil and Gas Exploration and Production Reporting Segment [Member]
Impaired Long Lived Assets Held and Used [Line Items]
Cost-method investment	1	87	12	91
Oil and Gas Exploration and Production Reporting Segment [Member] | U.S. onshore [Member]
Impaired Long Lived Assets Held and Used [Line Items]
Long-lived assets held for use	2		81	100
Oil and Gas Exploration and Production Reporting Segment [Member] | Gulf Of Mexico [Member]
Impaired Long Lived Assets Held and Used [Line Items]
Long-lived assets held for use		93	67	93
Midstream Reporting Segment [Member]
Impaired Long Lived Assets Held and Used [Line Items]
Long-lived assets held for use	$ 1	$ 3	$ 6	$ 3